The present invention relates to load-supporting structures. More particularly, the present invention relates to columns and methods for supporting compressive loads via contained pressurization of a filler material within a column.
Compression members are subject to some of the same failure modes as tension members. For example, members loaded in compression along their centroidal axis will deform until the elastic limit of the material is reached at which point they may plasticly deform or fracture.
However, as the longitudinal length of the compression member increases relative to its cross-sectional dimension, the compression member becomes susceptible to a unique failure mode known as column buckling. Buckling is the result of various influences including material imperfections and variations, slight eccentricities or movements in the location of the compressive load, and other factors. While there is no clear point at which a compression member becomes subject to buckling failure, compression members having a length greater than about ten times their smallest cross sectional width may be analyzed for this failure mode.
A column can buckle quickly and without warning, severely weakening and possibly destroying the structure of which it supports. Accordingly, columns are typically designed such that the maximum anticipated loading will be less than the critical buckling load (the load at which buckling will occur).
To prevent buckling, the cross-sectional dimension of the column is typically sized to provide adequate buckling resistance. While effective, increasing the size of the column may result in a heavier and more costly member. Alternatively, secondary support structures may be used in conjunction with the column. For instance, with architectural structures, columns may be reinforced with lateral bracing to avoid the unsupported spans that may result in buckling failure. In other applications, the restraint method used to secure the column ends (e.g., fixed, guided, pinned) may be selected to provide greater buckling resistance. Another option is to avoid or minimize compressive failure by the use of less conventional structures, e.g., catenary suspensions. However, these alternatives may also result in more complicated, costly, and heavier structures.
The use of reinforced concrete columns is also known for construction/architectural applications. However, such columns often require on-site fabrication which may include the forming of molds and the placement of reinforcing rods. Thus, assembly time and expense may be significant.
One column apparatus that seeks to address buckling failure is found in U.S. Pat. No. 4,685,253 to Bitterly. Bitterly describes a pressure tube, which, in one embodiment, has a cable extending between its longitudinal ends. The cable is tensioned when the column is preloaded, i.e., pressurized by an external pressurization system. The internal pressure is reacted by hoop stress in the cylindrical wall of the tube. When compressive loads are placed on the Bitterly apparatus, it can support forces up to the corresponding preload without buckling.
While effective, some embodiments of Bitterly require the cable to prevent ejection of the piston from the tube during pressurization. Thus, in multiple column configurations, the length of the cable must be controlled to ensure each column apparatus has substantially the same overall length. Moreover, the ends of the cable must be adequately secured to prevent ejection of the piston.
Further, the pressure produced in the Bitterly column appears to be reacted mostly or entirely through tangential stress in the wall of the column. As a result, the wall thickness must be selected accordingly.
Another column apparatus is described in U.S. Pat. No. 5,555,678 to Schoo. Schoo uses a highly pressurized column wherein the internal pressure brings about internal longitudinal tensile stress. When the column is then subjected to an external compressive load, the resultant state of stress is described as the composition of both states considered independently, as deduced from the principle of superposition.
In one embodiment, a column assembly operable to support a compressive load is provided. The column assembly includes a tube member having a first longitudinal end and a second longitudinal end. A first endcap operable to substantially seal the first longitudinal end of the tube member is also provided as is a second endcap operable to substantially seal the second longitudinal end of the tube member. The second endcap may be longitudinally movable relative to the tube member. The tube member, the first endcap, and the second endcap enclose a volume. The column assembly further includes a filler material operable to substantially fill the volume, wherein application of the compressive load across the first endcap and the second endcap results in increased pressurization of the filler material.
In another embodiment, a column assembly for supporting a compressive load is provided where the column assembly includes a cylinder assembly. The cylinder assembly includes: a tube member having a longitudinal length and an outer surface; and at least one reinforcing member circumscribing at least a portion of the outer surface of the tube member. The column assembly may also include a first endcap adapted to substantially cover a first longitudinal end of the tube member and a second endcap adapted to substantially cover a second longitudinal end of the tube member. In some embodiments, the second endcap is longitudinally movable relative to the tube member. Preferably, the tube member, the first endcap, and the second endcap enclose a volume that may be filled with a filler material. The filler material is operable to convert at least a first portion of the compressive load into tangential stress within a wall of the tube member.
In still another embodiment of the invention, a method for supporting a compressive load is provided. The method includes providing a column assembly having a tube member with an outer diameter and a longitudinal length, the longitudinal length terminated by a first longitudinal end and a second longitudinal end of the tube member. The column assembly further includes a reinforcing member surrounding the outer diameter along at least a portion of the longitudinal length. A first endcap adapted to substantially cover the first longitudinal end of the tube member is also provided as is a second floating endcap adapted to substantially cover the second longitudinal end of the tube member. The tube member, the first endcap, and the second floating endcap preferably substantially enclose a volume. The method also includes filling the volume with a filler material. By then applying the compressive load between the first endcap and the second floating endcap, a pressure of the filler material within the volume is increased. The method also includes generating tangential stress in the tube member in response to the increased pressure of the filler material.
In still yet another embodiment of the invention, a cylinder assembly is provided that includes: a hollow tube member having a longitudinal length and an outer surface; and one or more reinforcing members circumscribing at least a portion of the outer surface between a first longitudinal end of the hollow tube member and a second longitudinal end of the hollow tube member.
The above summary of the invention is not intended to describe each embodiment or every implementation of the present invention. Rather, a more complete understanding of the invention will become apparent and appreciated by reference to the following detailed description and claims in view of the accompanying drawings.